• Journal of the Korean Society of Safety
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• v.25 no.6
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• pp.128-136
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• 2010

In according with concrete structural design standard, it is common designing flexure reinforcement concrete to induce tension failure. So reinforcing ratio is limited to inducing tension failure. And maximum reinforcing ratio is regulated to protecting concrete compression strength caused by over reinforced building. Minimum reinforcing ratio is also limited in designing standard to protecting brittle failure as extremely using less reinforcing bar. But in minimum reinforcing ratio it is extremely conservative or it is sometimes impossible to induce stable tension-failure because they are depending on yield failure and experienced method and concrete designing standard strength. Therefore the purpose of the present paper is to evaluate the flexural behavior of minimum steel ratio of reinforced concrete of beams and to propose the guide-line of equation of minimum steel ratio by performing static flexural test of 16 beams according to size effect, number of steel, yielding stress of steel, and concrete compressive strength which are presumed effective variables. From experimental results, the equation of minimum steel ratio was newly proposed considered size effect.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.3
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• pp.35-44
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• 2017

In this study, steel fiber-reinforced concrete beams with ordinary steel reinforcements, that are below minimum steel reinforcement amount specified in domestic concrete structure design code, were tested in flexure until failure. Steel reinforcement ratio considered were 44%, 66%, 78% and 100% of the minimum steel reinforcement. Considered steel fiber volume fractions were 0.25%, 0.50%, 0.75% and 1.00%. In results, it is confirmed that steel fibers greatly improve crack performance. Also, the steel fibers contributed to increment in yield load not in ultimate load. But the increment was not greater than the reduction by steel reinforcement reduction. The use of steel fibers in RC beams lightly reinforced below the minimum reinforcement ratio specified design code reduced ductility greatly. Consequently, steel reinforcement ratio in steel fiber-reinforced beams lightly reinforced below the minimum steel reinforcement should be increased in order to enhance proper ductility.

• Advances in Computational Design
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• v.3 no.1
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• pp.49-69
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• 2018

This paper shows an optimal design for reinforced concrete rectangular combined footings based on a criterion of minimum cost. The classical design method for reinforced concrete rectangular combined footings is: First, a dimension is proposed that should comply with the allowable stresses (Minimum stress should be equal or greater than zero, and maximum stress must be equal or less than the allowable capacity withstand by the soil); subsequently, the effective depth is obtained due to the maximum moment and this effective depth is checked against the bending shear and the punching shear until, it complies with these conditions, and then the steel reinforcement is obtained, but this is not guaranteed that obtained cost is a minimum cost. A numerical experimentation shows the model capability to estimate the minimum cost design of the materials used for a rectangular combined footing that supports two columns under an axial load and moments in two directions at each column in accordance to the building code requirements for structural concrete and commentary (ACI 318S-14). Numerical experimentation is developed by modifying the values of the rectangular combined footing to from "d" (Effective depth), "b" (Short dimension), "a" (Greater dimension), "${\rho}_{P1}$" (Ratio of reinforcement steel under column 1), "${\rho}_{P2}$" (Ratio of reinforcement steel under column 2), "${\rho}_{yLB}$" (Ratio of longitudinal reinforcement steel in the bottom), "${\rho}_{yLT}$" (Ratio of longitudinal reinforcement steel at the top). Results show that the optimal design is more economical and more precise with respect to the classical design. Therefore, the optimal design presented in this paper should be used to obtain the minimum cost design for reinforced concrete rectangular combined footings.

• Computers and Concrete
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• v.8 no.4
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• pp.445-463
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• 2011

In the design of reinforced concrete (RC) beams, apart from providing adequate strength, it is also necessary to provide a minimum deformability even for beams not located in seismic regions. In most RC design codes, this is achieved by restricting the maximum tension steel ratio or neutral axis depth. However, this empirical deemed-to-satisfy method, which was developed based on beams made of normal-strength concrete (NSC) and normal-strength steel (NSS), would not provide a consistent deformability to beams made of high-strength concrete (HSC) and/or high-strength steel (HSS). More critically, HSC beams would have much lower deformability than that provided previously to NSC beams. To ensure that a consistent deformability is provided to all RC beams, it is proposed herein to set an absolute minimum rotation capacity to all RC beams in the design. Based on this requirement, the respective maximum limits of tension steel ratio and neutral axis depth for different concrete and steel yield strengths are derived based on a formula developed by the authors. Finally for incorporation into design codes, simplified guidelines for designing RC beams having the proposed minimum deformability are developed.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.04a
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• pp.485-490
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• 2000

This paper describes the application of discretized continuum-type optimality criteria (DCOC) for minimum-cost design of the reinforced concrete frame structures consisting of beams and columns. The cost of construction as objective function which includes the costs of concrete, reinforced steel and formwork is minimized. The design constraints include limits on the maximum deflection at a prescribed node, bending and shear strengths in beams, uniaxial bending strength of columns according to design codes(CEB/FIP, 1990). In the first stage, only beams with uniform cross-sectional parameters per span are considered. But the steel ratio is allowed to vary freely. The cross-sectional parameters and steel ratio in each column are assumed to be uniform for practical reasons. Optimality criteria is given based on the well known Kuhn-Tucker necessary conditions, followed by an iterative procedure for designs when the design variables are the depth and the steel ratio. The versatility of the DCOC technique has been demonstrated by considering numerical examples which have one-bay four-storey frame.

• Journal of the Korea Concrete Institute
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• v.26 no.2
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• pp.181-188
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• 2014

In this study, an interactive analysis considering column-pile interaction is performed on the basis of an equivalent base spring model for supplementing virtual fixed point design of bent pile structures. Through this analytical method, the application of the minimum steel reinforcement ratio of the pile (0.4%) is analyzed by taking into account the major influencing parameters. Furthermore, the limit depth for steel reinforcement ratio is proposed through the relationships between column and pile conditions. To obtain the detailed information, it is found that an interactive analysis is intermediate in theoretical accuracy between the virtual fixed point model analysis and full-modeling analysis. Base on this study, it is also found that the maximum bending moment is located within cracking moment of the pile when material nonlinearity is considered. Therefore, the minimum steel reinforcement ratio is appropriately applicable for the optimal design of bent pile structures. Finally, the limit depth for steel reinforcement ratio ($L_{As=x%}$) is proposed by considering the field measured results. It is shown that the normalized limit depth ratio for steel reinforcement ratio ($L_{As=x%}/L_P$) decreases linearly as the length-diameter ratio of pile ($L_P/D_P$) increases, and then converges at a constant value.

• Journal of Welding and Joining
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• v.18 no.6
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• pp.83-88
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• 2000

Variation of welded-joint hardness and tensile strength of a accelerated-cooled fine-grained ferritic-pearlitic steel with heat input was investigated. In a weld heat-affected zone, a softened zone was formed and it had lower hardness than that of a base metal. While the width of a softened zone increased continuously with an increase of heat input up to 100kJ/cm. the minimum hardness in a softned zone was almost constant after a continuos decrease up to 60KJ/cm. Because of a softened zone, the welded-joint was fractured in the HAZ and its maximum reduction of tensile strength was about 20%. Measured welded-joint tensile strength and calculated minimum tensile strength in a welded-joint was almost same, which means that the plastic restraint of a softened zone did not occur in this experiment. It is believed that as a softened zone width-to-specimen thickness ratio is as high as 2~6 in this experiment, the plastic restraint effect does not occur. Theoretical analysis shows that the plastic restraint effect occurs only when the ratio is below 0.5.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.4
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• pp.396-402
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• 2021

A cross section in RC flexural members must be designed to satisfy flexural strength and ductility requirements simultaneously. In design provisions, ductile behavior is ensured by a sufficient reinforcement ratio or depth of the neutral axis. If the reinforcement ratio is less than the balanced reinforcement ratio, ductile behavior is secured, and this value is theoretically the maximum reinforcement ratio. But for a cross section with less steel, brittle failure can occur regardless of ductile behavior because of unqualifying a cracking moment. Recently, designs with a minimum steel ratio have been increasing along with the use of high-strength material, so in design provisions, a minimum amount of reinforcement is suggested. In the KCI(2012) standard, a minimum amount of reinforcement was suggested in terms of strength of steel and concrete. But in the revised KCI(2017) standard, a minimum amount of reinforcement was suggested by a relationship between the design flexural strength and cracking moment indirectly. This code can reflect the effect of cover thickness, but a material model must be defined. Therefore, the minimum amount of reinforcement in KCI(2012) and KCI(2017) was examined, and a rational review method was studied by parametric analysis.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1988.05a
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• pp.46-48
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• 1988

The effect of cold reduction ratio on magnetic properties of 45% Ni-Fe permalloy was studied. To know the relationship between the crystal orientation and the magnetic properties, the pole figure was measured by X-ray diffraction method. In the case of single rolled reduction, the coercive force decreased with cold reduction ratio monotonically, but the maximum permeability, induction and squreness increased drastically. In the case of double rolled reduction (total reduction ratio is 90%), the saturation and residual induction increased slightly with secondary reduction ratio, but the maximum permeability and the coercive force had the maximum and the minimum value at the 50/50% reduction ratio respectively. And strong {100} <100> pole was developed by increasing the cold reduction ratio.

• Journal of the Korea Concrete Institute
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• v.27 no.5
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• pp.501-510
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• 2015

Composite construction of precast concrete and cast-in-place concrete is currently used for the modular construction. In this case, the use of steel fiber reinforced concrete (SFRC) could be beneficial for precast concrete. However, the shear strength of such composite members (SFRC and cast-in-place concrete) is not clearly defined in current design codes. In the present study, steel fiber composite beam tests were conducted to evaluate the effect of steel fibers on the composite members. The test variables are the area ratio of SFRC and shear reinforcement ratio. The test results showed that when minimum horizontal shear reinforcement was used, the shear strength of composite beams increased in proportion to the area ratio of steel fiber reinforced concrete. However, because of the steel fiber, the composite beams were susceptible to horizontal shear failure. Thus, minimum horizontal shear reinforcement is required for SFRC composite beams.